Go with the 390, it's so close at 1080p. Anything above 1440 it starts to get close to the gtx 980 (If you OC the 390).
I just bought the sapphire nitro 390 and in firestrike I beat a gtx 980. I am comparing overclocked to non-OC but the price difference between a 390 and 980 is huge.
People hate it when you talk future proof, but the 390 with 8gigs of ram and better performance at higher resolutions is more future proof.